Load the store of combobox while intializing the window

Hi

I've a window. In that window i've one combobox witha store. I want to mask the window until the store completes loading data. This i can achieve by writing this.setLoading(true) in store before load and this.setLoading(false) in load.But When i'm using above approach the mask is displaying after clikcing on the combo trigger. That means store is getting loading after clicking on the trigger. Instead of that i want to load the store while intializing the window.How can i achieve this?